The Larmor precession of a neutral spinning particle in a magnetic field confined to the region of a one dimensional-rectangular barrier is investigated for both a nonrelativistic and a relativistic incoming particle. The spin precession serves as a clock to measure the time spent by a quantum particle traversing a potential barrier. With the help of general spin coherent state it is explicitly shown that the precession time is equal to the dwell time in both the nonrelativistic and relativistic cases. We also present a numerical estimation of the precession time showing an apparent superluminal tunneling.
We revisit the notions of the quantum-mechanical sojourn time in the context of the quantum clocks to enquire whether the sojourn time be clocked without the clock affecting the dynamics of the wave motion. Upon recognizing that the positivity of conditional sojourn time is not ensured even in the case of physically co-evolving clock mechanisms, we trace its origins to the non-trivial inadvertent scattering arising from the disparity, however weak, engendered by the very clock potential. Specifically, our investigations focus on the Larmor spin rotation-based unitary clock where the alleviatio…
A tunable feedback-controlled magnetic trap for a magnet in free fall
Johannes Gutenberg University（约翰内斯·古腾堡大学）；Helmholtz-Institute, GSI Helmholtzzentrum fur Schwerionenforschung（亥姆霍兹重离子研究所(GSI)）；Leibniz University Hannover (LUH)（汉诺威莱布尼茨大学）；Technology and Engineering Center for Space Utilization, Chinese Academy of Sciences（中国科学院空间应用工程与技术中心）；Peking University（北京大学）；University of California, Berkeley（加州大学伯克利分校）
Tunneling time, time needed for a quantum particle to tunnel through a potential energy barrier, can be measured by a duration marker. One such marker is spin reorientation due to Larmor precession. With a weak magnetic field in $z$ direction, the Larmor clock reads two times, $τ_y$ and $τ_z$, for a potential energy barrier along the $y$ axis. The problem is to determine the actual tunneling time (ATT). B{ü}ttiker defines $\sqrt{τ_y^2 + τ_z^2}$ to be the ATT. Steinberg and others, on the other hand, identify $τ_y$ with the ATT. The B{ü}ttiker and Steinberg times are based on average spin compo…
